Here are a couple of 100 yard targets with bench rest groups I fired with a couple of prewar Mosin hex receiver 91/30's. In my several years of dinking around with them I never found a Mosin with a decent barrel that wouldn't group sub 2MOA from the bench with surplus ammo. Sometimes one may need to make a metal shim to place underneath the rear tang where old wood and too much torque on the rear action screw has caused the tang to sink in too far, but other than that they shoot well.
In the 5 years I've been in charge of our club's military matches I've only seen a couple of Mosins in competition and I'm sure it's because of their primitive trigger that you can't do a whole lot with as far as improving the pull. They almost never wind up in the winner's circle. However, stock Mosin's are usually regarded as being more accurate out of the box than a 98 Mauser in like condition, and I've found this to be true in my experience with both guns.
Wes, only shooting will prove whether or not the .308 diameter Sierra's will shoot well. Sometimes the bore diameter on these guns is .310 and other times it's anybody's guess - european military rifles are famous for inconsistent bore diameters. A friend had some 170 grain .30-30 bullets laying around and they made a very good 100 yard load for his gun, so I know .308 bullets will work at least part of the time. Anyway, here are the two groups I mentioned. They were fired with 147 grain Czech light ball corrosive surplus ammo. The top group measured 1 3/4 and the bottom one 1 7/8 even with the flyer.
Here is one of the guns involved. I had to have eye surgery in '08 that ended my career with heavy recoiling shoulder guns, so this one and all the other vintage military rifles in my safe were sold. But I sure loved them. This one is a 1935 hex receiver that I refinished.
They're a barrel of fun. Enjoy them.
Jer